CI: Add a separate CI job on Ubuntu to test geopandas v0.x

.github/workflows/ci_tests.yaml

@@ -79,6 +79,15 @@ jobs:
             pandas-version: ''
             xarray-version: ''
             optional-packages: ' contextily geopandas ipython pyarrow rioxarray sphinx-gallery'
+          # The job below is for testing geopandas v0.x on Ubuntu.
+          # The python-version here can't be the versions in the matrix.python-version
+          # defined above. Otherwise, other jobs will be overridden by this one.
+          - os: 'ubuntu-latest'
+            python-version: '3.11'  # Can't be 3.10 or 3.12.
+            numpy-version: '1.24'
+            pandas-version: ''
+            xarray-version: ''
+            optional-packages: ' geopandas<1'
 
     timeout-minutes: 30
     defaults: